1. Field of the Invention
The present invention relates to a contact lens formed from a polymer based on 2,3-dihydroxypropyl methacrylate (GMA) that has high water content and high water balance. The present invention also relates to methods of making and using such contact lenses. The present invention also relates to polymers and hydrogels of GMA and to methods of making and using such polymers.
2. Description of the Related Art
The literature teaches that high water content lenses are susceptible to dimensional changes during wear because they tend to lose a higher percent of water (dehydrate) relative to lenses of lower water content. Further, the ability to regain the lost water (rehydrate) is important to the dimensional stability of a contact lens. If a lens material absorbs water more rapidly, then the lens will more closely return to a water-saturated state during each blink, when the lens is bathed in tear fluid. Therefore, as a lens begins to dehydrate, a characteristic of rapid rehydration is extremely advantageous for maintaining saturation and maximum stability.
Unfortunately, conventional contact lens development either has ignored the effect of rehydration rate upon lenses or has constructed lenses of materials with a less than optimal rate of rehydration.
U.S. Pat. No. 5,532,289, hereby incorporated by reference in its entirety, describes a family of copolymers useful for making contact lenses. The copolymers have improved ability to remain near their water saturated state during wear. In this patent, the inventors of the present invention describe a method for making contact lenses with improved dimensional stability based on copolymers of 2,3-dihydroxypropyl methacrylate (GMA) and 2-hydroxyethyl methacrylate (HEMA). The polymers contain between 20 and 90 mole percent of GMA and have a water content from about 40 to about 70% by weight. The dimensional stability of these lenses results from the ability of these hydrogels to strongly bind water.
In the ""289 patent, lenses made from this family of materials were shown, under in-vitro conditions, to be slow to dehydrate and fast to rehydrate, relative to all other soft lens materials. The times it took a lens to dehydrate to 10% of its water weight and rehydrate back to saturation were combined into a factor called xe2x80x9cwater balancexe2x80x9d. This xe2x80x9cwater balancexe2x80x9d value can be used to compare commercial lens materials, regardless of water content and as a guideline, by practitioners, in selecting an appropriate lens material for a patient. This patent also emphasizes the ability to remain near or at saturation as a key to dimensional stability in a soft lens.
Clinical studies by Businger in Contact Lens Spectrum, August 1995, pp. 19-25 and die Kontaklinsen 7-8, 4 (1997) support the laboratory findings on water retention and lens stability. These studies report that lenses made from hioxifilcon A (p-GMA/HEMA, 59% water) were preferred by the largest margin of test subjects because of comfort and visual acuity. These lenses showed the highest dimensional stability and the best of both low-contrast and high-contrast visual acuity during wear cycles of 14 hours, over a period of 30 days, over other conventional contact lenses irrespective of water content.
The literature teaches that the water content of GMA/HEMA copolymers increases, from an initial 38% for p-HEMA, with increasing concentration of GMA. See, Yasuda, et. al., Journal of Polymer Science: Part A1, 4, 2913-27 (1966) and Macret et. al., Polymer, 23(5) 748-753 (1982), which describes hydrogels based on HEMA and GMA.
Refojo, Journal of Applied Polymer Science, 9, 3161-70 (1965), describes hydrogels of high water content made from GMA. The polymer are made by polymerization in bulk or in water solution. Also, high water content hydrogels of copolymers of GMA and glycidyl methacrylate are described.
Wichterle, et. al., UK Patent GB 2196973A, reported the use of hydrophilic solvents, such as glycerol, dimethylformamide, and dimethylsulfoxide, in 2-HEMA blends primarily for the centrifugal casting of contact lenses.
The literature is significantly void of examples of p-GMA homopolymer and copolymers where the GMA content exceeds 80 mole percent, for use in contact lens application. While some of the literature described above discusses hydrogels based on GMA polymers, the literature fails to suggests to fabricate contact lenses from polymer of high GMA content; and certainly none of the literature suggests that contact lenses formed from polymers of at least 80 mole percent GMA could exhibit the outstanding and unexpected properties, including slow dehydration and fast rehydration, i.e., a high water balance, discovered by the present inventors.
Since polymers that contain 2,3-dihydroxypropyl methacrylate (GMA) show improved water retention capability (See Pescossolido et al., Contactologia, 15D, 64-7 (1993) and Benz et al., Contact Lens Spectrum July 1997, pp.40-46), the present inventors conceived that a polymer composed mostly of GMA should yield a contact lens with extraordinary dimensional stability and water retention. Overall lens performance, with respect to stability and water retention, should surpass any commercial available lens material. However, to date, the art has failed to suggest contact lenses formed of polymers having at least 80 mol percent GMA or method of making such lenses.
Accordingly, it is an object of the present invention to provide contact lenses formed from a material primarily composed of GMA.
It is also an object of the invention to provide methods of making and using such contact lenses.
Another object of the invention is to provide polymers with improved machining, useful for a spheric contact lens, a toric contact lens, a multifocal contact lens, and a bandage contact lens.
Another object of the invention is to provide a spheric contact lens, a toric contact lens, a multifocal contact lens, and a bandage contact lens with superior dimensional stability.
Another object of the invention is to provide a spheric contact lens, a toric contact lens, a multifocal contact lens and a bandage contact lens with superior water retention and water balance.
Another object of the invention is to provide a spheric contact lens, a toric contact lens, a multifocal contact lens and a bandage contact lens suitable for daily wear and extended wear modalities.
It is also an object of the invention to provide blanks for contact lenses, and finished and unfinished contact lenses having improved characteristics, such as high water content and high water balance.
In accordance with these and other objectives, there has been provided according to the present invention, a contact lens formed of a copolymer of more than 80 mole percent, generally more than 90 mol percent, of 2,3-dihydroxypropyl methacrylate and up to 20 mol percent, generally from 0.05 up to 10 mol percent of a reactive pyrrolidone, such as a N-alkenyl pyrrolidone, such as N-vinyl pyrrolidone, or alkoxy alkyl methacrylate of formula R1xe2x80x94Oxe2x80x94R2xe2x80x94MA, wherein R1 and R2 are independently alkyl groups of 1 to 6 carbon atoms, and MA is methacrylate.
There also has been provided in accordance with the present invention, a hydrogel of a polymer including more than 90 mole percent of units from 2,3-dihydroxypropyl methacrylate and up to 10 mol percent of N-vinyl pyrrolidone or alkoxy alkyl methacrylate of formula R1xe2x80x94Oxe2x80x94R2xe2x80x94MA, wherein R1 and R2 are independently alkyl groups of 1 to 6 carbon atoms and MA is methacrylate, wherein the polymer has a water content of at least 60% by weight of the polymer.
There is also provided a contact lens formed from a homopolymer of 2,3-dihydroxypropyl methacrylate, wherein the polymer has a water content of at least 60%, and a water balance of greater than about 8 relative to that of p-HEMA.
There is also provided in accordance with the present invention a method of making a polymer including more than 90 mol percent of units from 2,3-dihydroxypropyl methacrylate, comprising polymerizing 2,3-dihydroxypropyl methacrylate in the presence of a polar aprotic diluent.
There is also provided a method of making a contact lens, comprising polymerizing GMA and a comonomer in the presence of a polar aprotic diluent to form a copolymer, and forming the copolymer into a contact lens.
Further objects, features, and advantages of the present invention will become apparent from the detailed description of preferred embodiments that follows.